# wheel

> Talos 0.7 · Since 0.6

Use it in a scene entity's `components` list as `{ "type": "wheel", … }`. The contract writes the fields flat and refuses unknown keys.

## Fields

| Field | Type | Required | Default | Allowed values | Description |
|---|---|---|---|---|---|
| `radius` | `number` | no |  |  | Rolling radius, metres, greater than zero. A standalone wheel needs one; under a vehicle with a preset, the preset's wheel on the same corner fills it. |
| `width` | `number` | no |  |  | Tread width, metres, greater than zero. Absent: 0.6 × radius. |
| `suspension` | `VehicleSuspension` | no |  |  |  |
| `tyre` | `VehicleTyres` | no |  |  |  |
| `inertia` | `number` | no |  |  | Spin inertia, kg·m², greater than zero, for the `curve` tyre. Absent, derived from radius and width. |
| `steerable` | `number` | no |  |  | Under a vehicle: the fraction of its steering this wheel takes, 0..1. Absent: 1 at the front, 0 at the rear. |
| `driven` | `number` | no |  |  | Under a vehicle: its share of the drive, 0..1. Absent: 0 at the front, 1 at the rear. |
| `braked` | `number` | no |  |  | Under a vehicle: its share of the brakes, 0..1. Absent: 1. |
| `handbrake` | `boolean` | no |  |  | Under a vehicle: whether the handbrake reaches it. Absent: true at the rear. |
| `visuals` | `string[]` | no |  |  | More entities drawn as part of this wheel, by id: a tyre and a hub cap modelled beside an empty wheel mount, as a prefab kart has them. Each is moved with this wheel every tick (suspension, steering, and spin about the wheel's axle through the wheel's centre) on top of where the scene put it, keeping its own rotation and scale. Each must be on the same body as the wheel, neither the wheel nor above it, not below it (a child already turns with it), and drawn by one wheel only. Absent: only the wheel entity is drawn turning; nothing is matched by name. |

## Rules that can refuse it

- `vehicle-cannot-steer-or-brake`
- `vehicle-geometry`
- `vehicle-invalid`
- `vehicle-value-implausible`
- `wheel-invalid`
- `wheel.not-finite`